The third quest in the ElementalCraft tree ("Small Elemental Storage") requires an Element Container rather than a Small Element Container, which is not yet able to be obtained at this point of the mod's progression

The elemental craft section of quests is yet to be reworked. this will be fully fixed in future releases

Replaced the "Small Elemental Storage" quest item with a Small Element container for a future update.

For the meantime, you can bypass the quest with this command: /ftbquests change_progress (Playername) complete 5E029A2BA469F42D

This quest has been changed and will be fixed in a future update.